Rotor hubs made from thick composite flexures used on helicopters are subject to delamination failures which have strong correlation to the flapping (bending) excursions seen during operations. While these failure modes are benign, the flexure durability life varies with the aircraft usage. The ability to measure this usage (e.g., bending angle excursions) would allow for prediction of what remaining useful life until delamination initiation and enable improved logistical response. In some examples, fiber optic strain sensors can be mounted on a surface of a main rotor flexure to measure the loads in the flexure. Surface mounted sensors can be subjected to high values of strain. Although the sensors can be offset to experience a proportion of the total strain, the output of the sensors can be subject to crosstalk from other loading modes such as torsion. In addition, surface mounted sensors can be exposed to the environment and, consequently, potentially can be damaged.